[actions] Drop jdk 19, add 21-ea and use 20 ga

Author: hazendaz

.github/workflows/ci.yaml

@@ -26,7 +26,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macOS-latest, windows-latest]
-        java: [17, 19, 20-ea]
+        java: [17, 20, 21-ea]
         distribution: ['zulu']
       fail-fast: false
       max-parallel: 5